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000298_news@newsmaster….columbia.edu _Wed Nov 19 15:25:51 1997.msg
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From: jrd@cc.usu.edu (Joe Doupnik)
Newsgroups: comp.protocols.kermit.misc
Subject: Re: How fast will a 16550 go?
Message-ID: <meAFR3VIto6t@cc.usu.edu>
Date: 19 Nov 97 10:19:25 MDT
References: <HMvc0w8Z7WcC092yn@netcom.com>
Organization: Utah State University
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Xref: news.columbia.edu comp.protocols.kermit.misc:8084
In article <HMvc0w8Z7WcC092yn@netcom.com>, jhurwit@netcom.com (Jeffrey Hurwit) writes:
> I would like to use MS-Kermit on two mahines connected by a null modem
> cable to transfer files. What is the maximum safe speed of a 16650 FIFO
> UART?
----------
The venerable 8250 UART and its modern successor the 16550A UART,
and even more modern variations of the latter, all work to 115Kbps. That's
the UART part of things but there is a great deal more to affairs than that
single chip. For starters, there is wiring, and RS-232 uses an electrically
terrible scheme such that faster bit rates mean using much shorter lengths.
At 115Kbps I would suggest no more than a couple of feet of wiring, less
is better.
Then the software on both ends needs to be very quick in responding.
That implies lack of competition for cpu time and interrupts. MSK is fast.
Just don't load TSRs that eat cpu time. Finally there is the other competitor,
the disk system, and that can easily punch *big* holes in available cpu time.
SCSI (the full bus master variety, not the el cheapo port i/o boards) largely
solves that.
In the end, test to find out what your particular systems can take.
Joe D.